patch 8.2.4610: some conditions are always true

Problem:    Some conditions are always true.
Solution:   Remove the useless conditions. (closes #9993)
diff --git a/src/sign.c b/src/sign.c
index e1aae51..3d9c387 100644
--- a/src/sign.c
+++ b/src/sign.c
@@ -847,7 +847,7 @@
 	if (sign->se_lnum < line1)
 	    continue;
 	new_lnum = sign->se_lnum;
-	if (sign->se_lnum >= line1 && sign->se_lnum <= line2)
+	if (sign->se_lnum <= line2)
 	{
 	    if (amount != MAXLNUM)
 		new_lnum += amount;